IPS-105 fixes: "Bad CPU type in executable" error cross building capnp libs

buildcode/capnp.code

@@ -12,13 +12,37 @@ if [ -f "${LIB_DIR}/${LIB_NAME}" ]; then
     exit 0
 fi
 
-# We must whipe the repo. It seems to hold capnp build dependencies used in build that have been build in previous runs of make (even we `make clean`), which causes "bad CPU type" building the 2nd time for arm64.
-rm -rf "${TMP_DIR}/${REPO_NAME}"
-
 REPO_SRC_DIR="${TMP_DIR}/${REPO_NAME}/c++"
-#if [ ! -d "${REPO_SRC_DIR}" ]; then
+if [ ! -d "${REPO_SRC_DIR}" ]; then
 	git clone -b "${VERSION}" https://github.com/capnproto/capnproto.git
-#fi
+fi
+
+###########################################################################
+# Needed for build
+# Note: this cap'n proto isntallation is only used (and MUST only be used) 
+# for (cross) _building_ the cap'n proto static libs (i.e. it's the 
+# installation used by `--with-external-capnp` in the actual builds below). 
+# It is *not* used (and MUST NOT be used) anywhere else.
+###########################################################################
+CAPNPROTO_USED_FOR_BUILD_PREFIX="${TMP_DIR}/tmpLocal"
+mkdir -p "${CAPNPROTO_USED_FOR_BUILD_PREFIX}"
+CPNP_BINARY_USED_FOR_BUILD="${CAPNPROTO_USED_FOR_BUILD_PREFIX}/bin/capnp"
+
+if [ ! -f "${CPNP_BINARY_USED_FOR_BUILD}" ]; then
+	pushd "${REPO_SRC_DIR}"
+		autoreconf -i
+		./configure --prefix="${CAPNPROTO_USED_FOR_BUILD_PREFIX}"
+		make clean
+		make -j6
+		make install
+	popd
+fi
+
+export CAPNP=${CPNP_BINARY_USED_FOR_BUILD}
+
+###########################################################################
+# Build the actual libs
+###########################################################################
 
 export LDFLAGS="-arch ${ARCH}"
 export CC="$(xcrun --sdk ${SDK} -f clang) -arch ${ARCH} -isysroot ${SDK_PATH}"
@@ -26,8 +50,10 @@ export CXX="$(xcrun --sdk ${SDK} -f clang++) -arch ${ARCH} -isysroot ${SDK_PATH}
 
 pushd ${REPO_SRC_DIR}
 	autoreconf -i
-	./configure --host=${HOST} --prefix=${CURRENT_LIB_DIR} --enable-static=yes --enable-shared=no
+	./configure --with-external-capnp --host=${HOST} --prefix=${CURRENT_LIB_DIR} --enable-static=yes --enable-shared=no
 	make clean
 	make -j6
 	make install
 popd
+
+unset CAPNP